1. Field of the Invention
The present invention generally relates to an optical imaging lens. Specifically speaking, the present invention is directed to an optical imaging lens for the application of dual band of visible light as well as NIR (near infrared) for use in portable electronic devices such as mobile phones, cameras, tablet personal computers, personal digital assistants (PDA), vehicles, or rescue devices for recording videos.
2. Description of the Prior Art
The specifications of portable electronic devices change all the time and the key element—an optical imaging lens—develops concurrently so a good imaging quality is needed as well as a smaller size. As far as the imaging quality is concerned, the demands for better imaging quality are getting higher and higher with the development of optical technology. In addition to the thinner lens sizes, the imaging quality and performance are critical as well in the optical lens design field.
Besides, in different environments, the focal length of the optical imaging lens may be changed by different temperature, thereby affecting the imaging quality. Therefore, it is expected that the focal shift of the optical imaging lens is not susceptible to changes in different temperatures.
In addition, the applications of an optical imaging lens is not only limited to take pictures and to record videos but also for the environmental surveillance, the dashboard cameras, the VR trackers or the face recognition. With the increasing applications, one single device may need to install at least one visible light imaging lens as well as an NIR imaging lens at the same time. Such demands for the double imaging lens sets not only increase the cost as well as the complication of the device but also influence the appearance design of the device. Furthermore, the focal length of the visible light and the focal length of near-infrared in the optical imaging lens are usually different. In order to design an optical imaging lens that can receive visible light and near-infrared (NIR) simultaneously, the conventional technique is to use the voice coil motor (VCM) in the lens set module, to adjust the position of the sensor.
Regarding the above-mentioned issues, an optical imaging lens with low focal shift in different temperatures and with simplified dual band detection function that detecting visible light and near infrared (NIR), and further having good image quality and shortened lens length is the focus of this design improvement. The designing of the optical lens is not just scaling down the optical lens which has good optical performance, but also needs to consider the material characteristics and satisfy some practical requirements like assembly yield. Accordingly, it is more difficult to diminish a mini-lens than to diminish a conventional one. Therefore, how to reduce the total length of a photographic device, but still maintain good optical performance, is an important objective to research.